Question

Ten different letters of an alphabet are given. Words with five letters are formed from these given letters. Then, the number of words which have at least one letter repeated, is

(a) 69760 

(b) 30240

(c) 99748

(d) None of these

Answer 1

The correct option is (a) 69760

Explanation:

Total number of five letters words formed from ten different letters = 10 x 10 x 10 x 10 x 10 =10⁵ 

Number of five letters words having no repetition =10 x 9 x 8 x 7 x 6 = 30240 

.'. Number of words which have at least one letter repeated = 10⁵ - 30240 = 69760